High-speed networks are continually evolving. The evolution includes a continuing advancement in the operational speed of the networks. The network implementation of choice that has emerged is Ethernet networks physically connected over twisted pair wiring. Ethernet in its 10/100BASE-T form is one of the most prevalent high speed LANs (local area network) for providing connectivity between personal computers, workstations and servers.
High-speed LAN technologies include 100BASE-T (Fast Ethernet) and 1000BASE-T (Gigabit Ethernet). Fast Ethernet technology has provided a smooth evolution from 10 Megabits per second (Mbps) performance of 10BASE-T to the 100 Mbps performance of 100BASE-T. Gigabit Ethernet provides 1 Gigabit per second (Gbps) bandwidth with essentially the simplicity of Ethernet. There is a desire to increase operating performance of Ethernet to even greater data rates.
FIG. 1 shows a block diagram of a pair of Ethernet transceivers communicating over a bi-directional transmission channel, according to the prior art. An exemplary transmission channel includes four pairs of copper wire 112, 114, 116, 118. The transceiver pair can be referred to as link partners, and includes a first Ethernet port 100 and a second Ethernet port 105. Both of the Ethernet ports 100, 105 include four transmitter TX , receiver RX, and I/O buffering sections corresponding to each of the pairs of copper wires 112, 114, 116, 118.
Failure of the link between link partners can occur in many different ways. Generally, a reduction of signal to noise ratio of signals being communicated across the link can lead to failure of the link. This generally occurs due to either a reduction in signal power, or an increase in noise and/or interference. Signal power can be compromised due to excessive attenuation of the signal. Noise and/or interferences can be introduced due to, for example, electromagnetic interference. Other sources of noise and/or interference include jitter, time varying signal components, inter-symbol interference (ISI), residual echo, near end cross-talk (NEXT), far end cross-talk (FEXT).
The twisted copper wires can operate as antennas that are susceptible to receive electromagnetic interference (EMI). Generally, the EMI appears as a narrowband interference source to Ethernet receivers. Typically, Ethernet systems mostly rely on EMI protection that is provided by shielding, and by transmitting the information differentially to provide immunity against the common-mode characteristics of the EMI. Higher frequency EMI can be partially rejected by the filtering performed at the analog-front end (AFE) of the Ethernet receiver. Additionally, in the past, Ethernet systems had sufficient operating margin such that the EMI did not cause the link to fail.
However, the immunity of current Ethernet systems (higher frequency systems) to EMI is not sufficient, and the EMI can cause the link to fail, and be unable to transmit data. Suppression of EMI can be extremely challenging since the EMI usually appears at unknown times and with unknown frequency, bandwidth, power, modulation, duration, etc. Additionally, suppressing the EMI when the link is already transmitting data is extremely difficult since the EMI characteristics need to be determined very fast to be able to cancel the EMI before the link fails. Moreover, there is no training data to help detect and cancel the EMI since the link is transmitting real traffic.
It is desirable to have an apparatus and method for recovering a link between link partners as quickly as possible when a failure of the link has been detected.